.TH std::experimental::ranges::equal_to 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::experimental::ranges::equal_to \- std::experimental::ranges::equal_to

.SH Synopsis
   Defined in header <experimental/ranges/functional>
   template< class T = void >

       requires EqualityComparable<T> ||
                Same<T, void> ||                                            (ranges TS)
                /* == on two const T lvalues invokes a built-in operator
   comparing pointers */

   struct equal_to;
   template<>                                                               (ranges TS)
   struct equal_to<void>;

   Function object for performing comparisons. The primary template invokes operator ==
   on const lvalues of type T. The specialization equal_to<void> deduces the parameter
   types of the function call operator from the arguments (but not the return type).

   All specializations of equal_to are Semiregular.

.SH Member types

   Member type                                                   Definition
   is_transparent (member only of equal_to<void> specialization) /* unspecified */

.SH Member functions

   operator() checks if the arguments are equal
              \fI(public member function)\fP

std::experimental::ranges::equal_to::operator()

   constexpr bool operator()(const T& x, const T& y) \fB(1)\fP (member only of primary
   const;                                                equal_to<T> template)
   template< class T, class U >

       requires EqualityComparableWith<T, U> ||
                /* std::declval<T>() ==                  (member only of equal_to<void>
   std::declval<U>() resolves to                     \fB(2)\fP specialization)
                   a built-in operator comparing
   pointers */

   constexpr bool operator()(T&& t, U&& u) const;

   1) Compares x and y. Equivalent to return ranges::equal_to<>{}(x, y);.
   2) Compares t and u. Equivalent to return std::forward<T>(t) == std::forward<U>(u);,
   except when that expression resolves to a call to a builtin operator == comparing
   pointers.

   When a call to \fB(1)\fP or \fB(2)\fP would invoke a built-in operator comparing pointers of
   type P, the result is instead determined as follows:

     * Returns false if one of the (possibly converted) value of the first argument and
       the (possibly converted) value of the second argument precedes the other in the
       implementation-defined strict total ordering over all pointer values of type P.
       This strict total ordering is consistent with the partial order imposed by the
       builtin operators <, >, <=, and >=.
     * Otherwise (neither precedes the other), returns true.

   The behavior is undefined unless the conversion sequences from both T and U to P are
   equality-preserving (see below).

   Equality preservation

   An expression is equality preserving if it results in equal outputs given equal
   inputs.

     * The inputs to an expression consist of its operands.
     * The outputs of an expression consist of its result and all operands modified by
       the expression (if any).

   Every expression required to be equality preserving is further required to be
   stable: two evaluations of such an expression with the same input objects must have
   equal outputs absent any explicit intervening modification of those input objects.

.SH Notes

   Unlike std::equal_to, ranges::equal_to requires both == and != to be valid (via the
   EqualityComparable and EqualityComparableWith constraints).

.SH Example

    This section is incomplete
    Reason: no example

.SH See also

   equal_to function object implementing x == y
            \fI(class template)\fP

.SH Category:
     * Todo no example
